From: Ezekiel Newren <ezekielnewren@gmail.com>
Date: Thu, 23 Oct 2025 18:00:21 GMT
Subject: Re: [PATCH 3/3] rust: generate bindings via cbindgen
Message-ID: <CAH=ZcbADTLvTioBf+LYQej1G0biZM8s3-iJG+BZjnpxj+8NjsA@mail.gmail.com>
In-Reply-To: <20251023-b4-pks-rust-cbindgen-v1-3-c19b61b03127@pks.im>

On Thu, Oct 23, 2025 at 1:17 AM Patrick Steinhardt <ps@pks.im> wrote:
> +C_BINDINGS = c-bindings.h
> +
> +GENERATED_H += $(C_BINDINGS)
> +
> +$(C_BINDINGS): cbindgen.toml $(RUST_SOURCES)
> +       $(QUIET_CBINDGEN)cbindgen --output $@
> +

My preference is to store all generated header files from cbindgen
under interop/ that way we don't pollute the root of Git. It also
makes ignoring generated header files easier (if we choose to) since
we'd only need to specify `/interop/` in .gitignore. For platforms
that can't compile Rust how are they going to build C if they depend
on those generated headers?

> diff --git a/cbindgen.toml b/cbindgen.toml
> new file mode 100644
> index 00000000000..ba4b2d63672
> --- /dev/null
> +++ b/cbindgen.toml
> @@ -0,0 +1,7 @@
> +language = "C"
> +
> +# Don't include standard C headers. These are managed by "git-compat-util.h".
> +no_includes = true
> +
> +# Use plain structs instead of using typedefs.
> +style = "tag"

This is what my cbindgen.toml file looked like.
```
sys_includes = ["git-compat-util.h"]

autogen_warning = "/* Warning, this file is autogenerated by cbindgen.
Don't modify this manually. */"

language = "C"
no_includes = true
usize_is_size_t = true
style = "tag"
tab_width = 4

[parse]
parse_deps = false
```
tab_width is the number of spaces, there is no option to use a tab
character in cbindgen.

> diff --git a/ci/install-dependencies.sh b/ci/install-dependencies.sh
> index b7b3cf35edf..3bce6f47f87 100755
> --- a/ci/install-dependencies.sh
> +++ b/ci/install-dependencies.sh
> @@ -37,7 +37,7 @@ fedora-*|almalinux-*)
>                 MESON_DEPS="meson ninja";;
>         esac
>         dnf -yq update >/dev/null &&
> -       dnf -yq install shadow-utils sudo make pkg-config gcc findutils diffutils perl python3 gawk gettext zlib-devel expat-devel openssl-devel curl-devel pcre2-devel $MESON_DEPS cargo >/dev/null
> +       dnf -yq install shadow-utils sudo make pkg-config gcc findutils diffutils perl python3 gawk gettext zlib-devel expat-devel openssl-devel curl-devel pcre2-devel $MESON_DEPS cargo cbindgen >/dev/null
>         ;;
>  ubuntu-*|i386/debian-*|debian-*)
>         # Required so that apt doesn't wait for user input on certain packages.
> @@ -64,7 +64,7 @@ ubuntu-*|i386/debian-*|debian-*)
>                 make libssl-dev libcurl4-openssl-dev libexpat-dev wget sudo default-jre \
>                 tcl tk gettext zlib1g-dev perl-modules liberror-perl libauthen-sasl-perl \
>                 libemail-valid-perl libio-pty-perl libio-socket-ssl-perl libnet-smtp-ssl-perl libdbd-sqlite3-perl libcgi-pm-perl \
> -               libsecret-1-dev libpcre2-dev meson ninja-build pkg-config cargo \
> +               libsecret-1-dev libpcre2-dev meson ninja-build pkg-config cargo cbindgen \
>                 ${CC_PACKAGE:-${CC:-gcc}} $PYTHON_PACKAGE

cbindgen is a Rust crate and it should be specified in the Cargo.toml
under [build-dependencies] block. Also I think that we should convert
from using a Cargo crate to using a Cargo workspace, so that we can
generate multiple header files (1 per crate) rather than a monolithic
generated header. This is because cbindgen operates at the granularity
of a crate.